Exercise devices, and in particular weight training machines, typically include a mechanical member that the user moves along a prescribed path for exercise. Conventionally, movement of the mechanical member is resisted in some fashion to render the movement more difficult and thereby intensify the exercise. The most common means for providing resistance to movement of the mechanical member is a unit that connects the mechanical member with one or more weights such that the weights are raised in response to the movement of the mechanical member.
Often the weights of an exercise machine are provided in a stack; any or all of the weights (which are typically identical in weight) can be secured to a connecting rod that extends through the entire weight stack via apertures in the weights. The connecting member is then interconnected with the mechanical member, either directly or indirectly, via a one or more of belts, chains, cables, levers, or other means. Movement of the mechanical member by a user is resisted by the weight secured to the connecting rod.
In one commonly employed configuration, the weights are secured to the connecting rod via a selecting pin, which can be inserted through an aperture included in each weight or a gap between weights and into an opening in the connecting rod. Insertion of the connecting pin into a connecting rod aperture causes the portion of the weights in the stack above the pin (i.e., those weights positioned between the pin and the interconnecting belt) to travel as a substack with the connecting rod and thereby provide resistance to movement of the exercise arm; the portion of the weights in the stack below the pin (i.e., those weights positioned farther from the interconnecting belt than the pin) remain stationary and provide no resistance to movement of the exercise arm. Of course, the amount of weight providing resistance to the movement is equal to the weight of the substack of weights travelling with the connecting rod. The amount of resistive weight can be easily adjusted by repositioning the selecting pin in the connecting rod in a different weight or between different weights so that a different number of weights travel with the connecting rod.
Space limitations often restrict the number of weights that are included in a weight stack. Because it is desirable to provide exercise machines that can be comfortably used by virtually any user (which may include both weak or infirm individuals using the machine for rehabilitation and very strong individuals for whom substantial resistance is required), the weights typically provided are rather heavy. Also, generally the individual weights in a stack are of the same magnitude. As the weights in a stack are generally both heavy and uniform in magnitude, the incremental increase in resistance experienced by a user adding but a single weight to the travelling substack can be quite significant. Such an increase can be particularly onerous for novices, rehabilitation patients, elderly users, and others who lack strength.
One attempt to address the problem of an overly high incremental weight increase is offered in U.S. Pat. No. 4,834,365 to Jones. The Jones machine includes two weight stacks: one stack comprising conventional heavier weights; and one stack comprising much lighter weights. These stacks are positioned so that the stack of lighter weights resides directly above the stack of heavier weights. Both stacks share a common connecting rod to which a portion of their weights can be secured. When the mechanical member of the exercise machine is moved, the desired number of weights of both stacks travel with the connecting rod and provide resistance. The lighter weights contribute to the resistance experienced by the user and therefore provide more resistance magnitude options. For example, a rehabilitating patient may be exercising on a machine that has a large weight stack of twenty pound weights and a lighter weight stack of one pound weights. If the patient's rehabilitation is best served by a resistance of thirty pounds, he can add resistance in one pound increments with the heavier weight stack to a twenty pound weight from the heavier stack to total thirty pounds rather than being forced to proceed directly from twenty to forty pounds of resistance.
Another approach is discussed in U.S. Pat. No. 5,776,040 to Webb, which includes separate stacks of lighter (e.g., one-pound) and heavier (e.g., ten-pound) weights, each with its own connecting rod and pin. The weight stacks are positioned side-by-side. Each connecting rod is attached to its own belt, with the belts following similar paths over pulley assemblies that are coupled to a movement arm. By selecting weights from both weight stacks, the exerciser can select precisely an amount of weight desired for resistance.
In view of the foregoing, it may be desirable to provide additional weight systems that provide resistance in small increments.